1-carbalkoxy-4-substituted piperazines



Patented Dec. 26, 1950 l-CARBALKOXY-l-SUBSTITUTED PIPERAZINES Richard Joseph Turner, Somerville, and Hugh Wendell Stewart, Plainfield, N. J., assignors to American *Cyanamid Company,

New York,

N. Y., a corporation of Maine No Drawing. Application October 15, 1948, Serial No. 54,816

6-Claims. 1 This invention relates to new organic compounds and their preparation. More particularly it relates to 1-carbalkoxy-4-substituted piperazines.

The l-carbalkoxy piperazines of the present invention may be illustrated by the following eneral formula:

wherein R and R are members of the group consisting of hydrogen and lower alkyl radicals, R" and R' are hydrogen and aliphatic radicals and X is a member of the group consisting of oxygen, sulfur, and imino radicals. As used herein, the term lower alky radical means a radical of l to 4 carbon atoms.

In general, the compounds of the present in- H--N/ l-[I N-COO-alkyl wherein R and R are as previously defined or addition salts of such piperazines with any compound which is capable of introducing into the 4-position of the piperazine nucleus a group represented by wherein R and R'" and X are as previously defined. As starting material, we can use compounds such as l-carbethoxypiperazine; l-carbethoXy-2,5-dimethylpiperazine; 1' carbethoxy- 2,6-dimethylpiperazine; 1-carbethoxy 3,5 dimethylpiperazine; 1 carbomethoxypiperazine; 1 carbomethoxy 2,5 dimethylpiperazine; 1- carbomethoxy-2,6-dimethylpiperazine; l-carbomethoxy-3,5-dimethylpiperazine, and the like. In a reaction of this type wherein a halogen acid is liberated, it is usually desirable to have present an acid binding substance such as an alkali metal bicarbonate, alkali metal carbonate, or the like.

As intermediates to be reacted with the 1- carbalkoxypiperazines, we can use an alkali metal cyanate or a monoor dialkylcar'bamyl chloride to produce the 1-carbalkoxy-=l--carb amylpiperazines. In producing l-carbalkoXylthiocarbamylpiperazines, We can use asintermediates an alkali metal thiocyanate, an aliphatic isothiocyanate or a monoor dialkylthiocarbamyl chloride. The guanyl derivatives of l-carbalkoxypiperazines may be prepared by two methods: (1) by the reaction of a l-carbalkoxypiperazine salt with a cyanamide, and (2) by the reaction of a l-carbalkoxypiperazine with an S-alkylisothioureau salt. A suitable solvent in carrying out either process is water or aqueous alcohol.

The reaction, in general, is preferably carried out in solution, although it can be carried out as a fusion process. Temperatures of 20 to 110 C. are usually sufficient to complete the reaction in a reasonable time when water is used as the solvent. Generally, the reaction is carried out at 20 to about 0. when aqueous alcoholic solvents or hydrocarbon solvents, such as benzene, are used. The conditions under which the reaction is carried out are dependent both upon the group being introduced into the 4-position and upon the reactivity of the l-carbalkoxypiperazine. For instance, l-carbethoxypiperazine hydrochloride can be treated in aqueone solution with potassium thiocyanate at room temperature to give 1-carbethoxy-4-thiocarb amylpiperazine; when trans-1-carbethoxy-2,5- dimethylpiperazine hydrochloride is treated under similar conditions, no appreciable amount of trans-1-carbethoxy-4-thiocarbamyl 2,.5 dimethylpiperazine is produced. The latter may be obtained, however, by the heating of trans- :53 1carbethoXy-2,5-dimethylpiperazine hydrochloride without an added solvent in the presence of potassium thiocyanate to the fusion point of the mixture.

Some of the compounds in the present application are active antifilarial agents and may be useful in the treatment of filariasis. Other compounds produce sedation in animals stimulated with an agent such as ephedrine, and still other compounds show analgesic activity. In general, the compounds are characterized by their relatively low toxicity.

The following examples show in greater detail the preparation of illustrative l-carbalkoxy-4- substituted piperazines within the scope of the present invention.

Example 1 To a solution of 19.4 parts of l-carbetho-xypiperazine in 25 parts of water is added 9.7 parts of potassium thiocyanate, and the reaction mixture is allowed to stand for about four hours. It is then evaporated under reduced pressure to a viscous residue. On the addition of 16 parts of absolute ethyl alcohol to the residue, a white solid forms. This solid is separated by filtration and the ethanol filtrate is then evaporated. On chilling, a solid residue is obtained. The solid is further purified by recrystallization from isoprop-yl acetate. The product, l-carbethoxy-4- thiocarbarnylpiperazine, melts at 109.0-1l0.5 C.

Example 2 A solution of 82 parts of potassium cyanate in I 75 parts of water is added to a solution of 195 parts of l-carbethoxypiperazine hydrochloride in 125 parts of water. After standing at room temperature for twenty-four hours, the mixture is evaporated to dryness. The residue is extracted with liloparts of absolute ethanol, acidified with hydrochloric acid and then it is evaporated to about 125 parts of ethanol. On cooling, the product crystallizes from solution. The precipitate, after isolation, is further purified by recrystallization from ethanol using activated charcoal. A yield of 146 parts of 1-carbethoxy-4-carbamylpiperazine, melting at l6l-162 C., is obtained.

Example 3 To a solution of 63.3 parts of 1-carbethoxypiperazine in 175 parts of benzene there is slowly added at --i0 C., with cooling and stirring, 34.8 parts of ethyl isothiocyanate. The mixture is stirred at refluxing temperature for one-half hour. The benzene solution is concentrated and the product is precipitated by the addition of petroleum ether. On recrystallization from a mixture of isopropyl acetate and petroleum ether, the product, 1-carbethoxy-l-ethylthioc'arbamylpiperazine, melting at 91-91.5 0., is obtained.

Example 4 4 methylpiperazine, may be prepared from ethyl chlorocarbonate and trans-2,5-dimethylpiperazine by the method described by Moore, Boyle, and Thorn, Journal of the Chemical Society, 39 (1929). It distills at 112 at 10 mm.

Example 5 To a solution of 56 parts of trans-l-carbethoxy-2,5-dimethylpiperazine in 210 parts of absolute ether is added anhydrous hydrogen chloride until the reaction mixture is acidic to Congo red paper. The hydrochloride salt obtained is isolated by filtration, ground and mixed well with 32 parts of potassium thiocyanate. The mixture is then heated at 130 C. for five minutes. The reaction becomes slightly exothermic at about 110 C. After cooling, the reaction product is slurried in boiling isopro-pyl acetate, the potassium chloride is removed by filtration and the filtrate is diluted with petroleum ether. On cooling, trans- 1 -carbethoxy- 2,5 -dimethyl- 4 -thiocarbamylpiperazine is obtained which has a melting point of 94.595 C.

Example 6 To a solution of 78 parts of ethyl alcohol in 100 parts of water are added .1.8 parts of s methylisothiourea sulfate and. 56 parts of trans-1- carbethoxy 2,5 dimethylpiperazine. The reaction mixture is refluxed on a steam bath until the evolution of methyl mercaptan ceases. The reaction mixture is dehydrated by azeotropic distillation with benzene. The resulting solid, trans-l-carbethoxy -2,5- dimethyll-guanylpiperazine sulfate. may be further purified by crystallization in the usual manner,

Example 7 A solution of 18.5 parts of l-diethylcarbamylpiperazine in parts of benzene is added to 10.8 parts of ethyl chlorocarbonate and 16.6 parts of sodium carbonate and the reaction mixture refluxed for 15 hours. The white solid obtained is separated from the reaction mixture by filtration and the filtrate exaporated under reduced pressure. The viscous residue obtained is dis tilled under reduced pressure to give l-carbethoxyl-diethylcarbamylpiperazine which boils at 179 C. at '7 mm. pressure.

We claim:

1. A l-carbalkoxypiperazine having the general formula:

wherein R, and R are members or the group consisting of hydrogen and lower alkyl radicals, R and R are members of the group consisting of hydrogen and alkyl radicals, and X is a member of the group consisting of oxygen, sulfur and imino radicals.

2. A l-carbalkoxypiperazine having the general formula:

R/II

wherein R" and R are members of the group consisting of hydrogen and alkyl radicals, and X is a member of the group consisting of oxygen, sulfur and imino radicals.

5 6 3. A 1-carba1koxy-4-dia1ky1thiocarbamy1piper 6. The compound 1-carbethoxy-4-diethy1carazine having the general formula: bamylpiperazine having the following formula:

R" s 01H;

N '1-1 11 N CO0aIkyl NJL H N -ooo*,m

n! CHHB in which R" and R' are alkyl radicals. RICHARD JOSEPH TURNER. 4. The compound 1-carbethoxy-4-thiocarbam- HUGH WENDELL STEWART. ylpiperazine having the following formula:

H S REFERENCES CITED g f H 4300mm The f o1 1owing references are of record in the H file of this patent: 5. The compound 1-carbethoxy-2,5-dimethyl- UNITED STATES PATENTS 4-guanylpiperazine having the following formula: 15 Number Name Date CH3 2,415,785 Buck Feb. 11, 1947 H NH l 2,415,787 Buck 1 Feb. 11, 1947 L H ILCOOCH 2,467,893 Kushner Apr. 19, 1949 2,467,894 Kushner Apr. 19, 1949 E E3 20 2,467,895 Kushner Apr. 19, 1949 2,472,496 Steward June 7, 1949 

1. A 1-CARBALKOXYPIPERAZINE HAVING THE GENERAL FORMULA: 